I'm in my first year of senior and it hasn't been all too difficult. As mentioned you're probably already doing senior work. Just don't do to your staff what you hated your seniors doing to you, and be reasonable with your expectations.

Not really. I was already working directly with managers and above as a Staff 2 on most of my projects, and I don't feel like their expectations of me changed much when I became a senior. Just maintain good relationships with them and you'll be fine.